netdev - Re: [RFC PATCH 0/3] Network stack, first user of SLAB/kmem

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Date:	Fri, 4 Sep 2015 18:45:13 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Alexander Duyck <alexander.duyck@...il.com>
cc:	Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	aravinda@...ux.vnet.ibm.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	iamjoonsoo.kim@....com
Subject: Re: [RFC PATCH 0/3] Network stack, first user of SLAB/kmem_cache
 bulk free API.

On Fri, 4 Sep 2015, Alexander Duyck wrote:
> Right, but one of the reasons for Jesper to implement the bulk alloc/free is
> to avoid the cmpxchg that is being used to get stuff into or off of the per
> cpu lists.

There is no full cmpxchg used for the per cpu lists. Its a cmpxchg without
lock semantics which is very cheap.

> In the case of network drivers they are running in softirq context almost
> exclusively.  As such it is useful to have a set of buffers that can be
> acquired or freed from this context without the need to use any
> synchronization primitives.  Then once the softirq context ends then we can
> free up some or all of the resources back to the slab allocator.

That is the case in the slab allocators.

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